This invention relates generally to an electromagnetic clutch for selectively causing torque to be transmitted between an input shaft and an output shaft.
In general, an electromagnetic clutch of the type under consideration comprises a rotor rotatable with one shaft, an armature rotatable with the other shaft, and a field assembly having a selectively energizable coil for causing magnetic flux to thread through a field shell. When the coil is energized, the flux cuts across air gaps between the field shell and the rotor and across an air gap between the rotor and the armature in order to attract the armature axially into frictional engagement with the rotor and thereby couple the two shafts for rotation in unison.
Although the clutch of the invention may be used in different applications, it is especially useful as a synchronizing clutch for causing two shafts to rotate at substantially the same speed prior to shifting gears, splines or other toothed members on the shafts into meshing engagement in order to establish a positive drive between the shafts. Fogelberg U.S. Pat. No. 4,561,520 discloses an electromagnetic synchronizing clutch in conjunction with the transfer case of a 4-wheel drive vehicle. While the Fogelberg clutch causes the two shafts to rotate at substantially the same speed prior to shifting of the toothed members into meshing engagement, the shifting itself is initiated through the use of a conventional mechanical linkage.